Syngas produced via the gasification of carbonaceous feedstock often includes a significant tar component. The tar component can include benzene, toluene, naphthalene, pyrene and indene, among others. These tars present a major concern in commercial gasification facilities as they clog and foul downstream equipment.
The destruction and/or removal of contaminating tars can be difficult with the effectiveness of tar removal strategies dependent on process parameters and the individual molecules. Simulations of thermal conversion of benzene, toluene and naphthalene have been reviewed in the literature and suggest that both significant residence times and elevated temperatures (as high as 1250° C.-around 1523 K) are necessary to obtain high levels of tar conversion.
A number of studies have examined the use of plasma to crack tar. For energy conversion processes, such as conversion of hydrocarbons into syngas, the best results have been obtained in non-thermal plasma (NTP) systems that utilize “warm”, gliding-arc plasmas, with gas temperatures in the 2,000 K-4,000 K range.
Plasma reforming of tars, modeled typically with naphthalene or toluene, has been studied using a variety of discharges including microwave, corona and gliding arc discharges. Although these studies demonstrated high removal efficiencies, their undesirable attributes, namely high specific energy input, unrealistic input gas, low tar concentration, low flow rate, and low energy efficiency, make them undesirable for industrial application.
Non-equilibrium plasma systems are known from the art and include those described in U.S. Pat. Nos. 8,603,403; 8,110,155; 7,867,457; 8,618,436; 5,960,026; 6,924,608; and 7,417,385, as well as Chinese patent 201722188 and French patent FR2775864.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.